Why does camstasia sometimes make a an hour video 90 Mb and other times 900mb?

So i recorded a stream of roughly an hour. it came out to 80 mb. i didnt have to edit anything.

Then i make another recording about an hour as well, and it does require edits, but it comes out to 900 mb under the same render settings? why is this? Do you have to do something to make all the edits converge, similar to combining layers in a paint program? This seems wildly inefficient and random, these numbers.

That's the strange part. All videos are of the same content. The only edits I do are clipping small segments out of the video before processing. That's why it makes no sense. At first I though the program was incredibly efficient, making such small file sizes. I don't understand.

I'm some cases, similar video length and almost identical content are making videos literally 10 times more MBs.